Minutely patterned structure

ABSTRACT

A patterned structure including a plurality of patterned sheet members which have respective configurations and which are partially superposed on each other and which cooperate with each other to define a plurality of voids. At least one of the sheet members includes a thin-walled portion whose thickness is smaller than a thickness of the other portion. The thin-walled portion is formed by etching the appropriate sheet member or members. The thin-walled portion of one sheet member engages the corresponding thin-walled portion or the other portion of the other sheet member or members.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a patterned structure having minuteslits, openings or other voids whose aspect ratio (ratio of the diameteror width to the thickness, i.e., diameter/thickness or width/thickness)is smaller than 1, and a method of producing such a minutely patternedstructure.

2. Discussion of the Prior Art

Patterned structures having extremely small slits, openings or othervoids, particularly, such patterned structures made of a metallicmaterial, have been used as electrical lead frames for LSI packages, andas various masking members, for example. Techniques for fabricating adouble-layer or bi-plane lead frame or similar product from two members,with improved density of the wiring formed thereon, are known accordingto various publications such as laid-open Publications 58-90752,60-92646, 60-103652, 60-107848, 60-206144, 60-227457 and 62-81739 ofunexamined Japanese patent applications. Generally, these techniques offabrication utilize press-forming or etching methods. These methods aredifficult to be practiced for forming slits, openings or other voidswhich have a small aspect ratio. Conventionally, therefore, the voidshaving a small aspect ratio are formed by ion-milling or laser-cuttingmethods.

Another technique for producing a patterned structure is disclosed inlaid-open Publication 51-40869, wherein a plurality of thin sheetshaving the same configurations are superposed on each other to form aplanar patterned assembly having a desired thickness.

However, such a planar patterned structure as indicated above suffersfrom extreme difficulty in precisely positioning the two or more sheetsrelative to each other, and therefore cannot provide a sufficiently highdegree of dimensional or configurational accuracy of the formed pattern.Further, the thickness of the patterned structure is determined by thetotal thickness of the constituent sheets that are superposed on eachother. Where the patterned structure has a portion or portions whosethickness should be accurately controlled, the desired thicknessaccuracy cannot be easily obtained. In the case of an electrical leadframe, the thickness or volume of resin, ceramic or other sealingmaterials increases with the thickness of the structure, i.e., totalthickness of the constituent sheets. In this case, the heat dissipationcharacteristic of the lead frame is accordingly deteriorated.

On the other hand, the conventional ion-milling and laser-cuttingmethods do not permit sufficient efficiency in forming the voids, andmay cause damage to the portions of the workpieces which should be keptintact. Further, these methods require extremely expensive equipment. Ifthe workpiece sheet is reduced to reduce the width of the slits or thediameter of the openings, the strength and the uniformity of thicknessof the prepared patterned structure tend to be reduced, and thepatterned structure cannot be easily processed for practicalapplication. Thus, the ion-milling and laser-cutting methods suffer fromdrawbacks in terms of the process to form the voids in the structure,and the physical properties and the dimensional and configurationalaccuracy of the structure.

In the alternative known method which uses two or more sheets having thesame configuration to prepare a patterned structure, it is considerablydifficult to establish precise alignment of the sheets relative to eachother for accurate dimensioning of the pattern. Further, since thethickness of the patterned structure is determined by the totalthickness of the sheets superposed on each other, it is difficult toprecisely control the thickness of the desired local portions of thestructure.

SUMMARY OF THE INVENTION

The present invention was developed in view of the prior art situationdescribed above. It is therefore a first object of the invention toprovide a patterned structure which has accurately dimensioned openings,slits or other voids whose aspect ratio is relatively small.

A second object of the invention is to provide a comparatively simplemethod suitable for producing the patterned structure, with relativelysimple equipment.

The first object may be attained according to one aspect of theinvention, which provides a patterned structure comprising a pluralityof patterned sheet members which are partially superposed on each otherand which cooperate with each other to define a plurality of voids. Thepatterned sheet members have respective areas at which the sheet membersare superposed on each other. At least a part of the area of at leastone of the patterned sheet members includes a thin-walled portion whosethickness is smaller than a thickness of the other portion of the atleast one patterned sheet member.

The second object may be attained according to another aspect of thepresent invention, which provides a method suitable for producing apatterned structure, which comprises the steps of: preparing a pluralityof patterned sheet members having predetermined configurations orshapes; forming a thin-walled portion on at least one of the patternedsheet members such that a thickness of the thin-walled portion issmaller than a thickness of the other portion of the above-indicated atleast one patterned sheet member; and superposing the patterned sheetmembers on each other such that at least the thin-walled portion of eachof the above-indicated at least one patterned sheet member engages thecorresponding thin-walled portion or the other portion of the otherpatterned sheet member or members.

According to the present invention, the plurality of patterned sheetmembers, preferably made of a metallic material, are first prepared soas to have desired outer configurations or profiles, depending upon adesired shape of a patterned structure to be produced. These patternedsheet members may be formed by various known methods such aspress-forming and ultrasonic cutting methods, and the methods forforming the sheet members are not bound by the specific patternedstructure to be produced. However, the patterned sheet members may bemost preferably formed by an etching method which uses etching masks.The etching process is less likely to cause a residual strain in theetched workpiece sheets, and assures high degree of dimensional andconfigurational accuracy of the sheets. For example, the etching masksmay consist of a resist which is resistant to an etching solution andwhich is suitably patterned by a photolithographic or precision-printingtechnique.

Then, at least a part of the surface area of at least one of thepatterned sheet members is subjected to an operation to reduce itsthickness. Namely, a thin-walled portion or portions is/are formed at adesired part or parts of the sheet member or members. The patternedsheet members are superposed on each other such that each thin-walledportion of one of the sheet members is in contact with the correspondingthin-walled portion or the other portion of the other sheet member ormembers. However, all the thin-walled portions of the patternedstructure need not be provided on only one of the sheet members. Some ofthe thin-walled portions may be provided on one of the sheet members,while the other thin-walled portions may be provided on the other sheetmember or members.

The thin-walled portions may be advantageously formed by suitable knownwet or dry etching operations. The desired thicknesses of thethin-walled portions are established by suitably determining oradjusting the etching conditions. The non-etched portions (otherthick-walled portions) of the sheet member or members are covered bysuitably patterned resist masks formed by a photolithographic,precision-printing or other method. Thus, the material is removed byetching from the appropriate parts of the sheet member or members, toform the thin-walled portions, such that a portion of the thickness ofthe sheet member or members is reduced. This etching to partially removethe material from the sheet members will be referred to as "halfetching".

Where the patterned sheet members are patterned by etching, the "halfetching" to form the thin-walled portions may be effected concurrently,by masking only one of the opposite surfaces of the sheet member so asto cover the appropriate local areas by a resist. It is also possible tofirst effect the half etching on at least one of the sheet members, andsubsequently effect an operation for establishing the desired outerprofiles of the sheet members.

While the thin-walled portions may be formed on only one of the sheetmembers, it is preferable that each sheet member has the thin-walledportion or portions, so that the thin-walled portions of the differentsheet members are held in contact with each other.

Where the two or more thin-walled portions are provided on each of thepatterned sheet members, it is desirable that these thin-walled portionshave different thicknesses. In the case where a planar patternedstructure is prepared by superposing two patterned sheet members on eachother, for example, each of the first and second sheet members has afirst thin-walled portion having a thickness which is one third of thesheet thickness, and a second thin-walled portion having a thicknesswhich is two thirds of the sheet thickness. In this case, the first andsecond sheet members are assembled such that the first thin-walledportion of the first sheet member and the second thin-walled portion ofthe second sheet member are in contact with each other, while the secondthin-walled portion of the first sheet member and the first thin-walledportion of the second sheet member are in contact with each other.

The patterned structure according to the present invention may be usedwithout securing the constituent sheet members to each other. However,the sheet members may be bonded together by suitable means such as anadhesive agent, spot welding or ultrasonic welding, in order to avoidseparation of the sheet members. The patterned structure has a surfacearea at which the sheet members are superposed on each other. Sometimes,this surface area includes a part whose thickness should not consist ofthe thicknesses of the two or more sheet members. In this case, the partin question should not include a thin-walled portion. Alternatively, thethin-walled portion or portions is/are provided on appropriate dummyportions of the sheet members, so that these dummy portions are cut offafter the sheet members are assembled into the patterned sheetstructure. All the portions of the patterned structure at which thesheet members are superposed on each other need not include athin-walled portion or portions. That is, the sheet member or membersmay include a bent or folded part or parts at which the sheet membersengage each other. Further, the thin-walled portions of the sheetmembers may be provided only at those parts or areas of the patternedstructure at or by which the sheet members are positioned relative toeach other, or at which the appropriate portions of the sheet memberslie in the same plane.

The half etching to form the thin-walled portions of the patterned sheetmembers according to the method of the invention as described aboveresults in reduced residual strain of the sheet members and improveddimentional and configurational accuracy of the patterned structure, ascompared with the conventional press-forming or other mechanicalmethods. Further, the half etching method according to the inventionfacilitates controlling the thicknesses of the patterned structure,reduces nicks and burrs or undesired raised areas, consists of acomparatively small number of process steps, and requires relativelysimple equipment.

The patterned structure constructed according to the invention hasimproved accuracy of positioning of the two or more sheet membersrelative to each other, owing to the engagement of the thin-walledportion or portions of one or more of the sheet members, with thecorresponding portion or portions of the other sheet member or members.The patterned structure may be suitably provided in the form of a planarstructure, which has suitably located minute openings, holes, slits orother voids having a small aspect ratio that cannot be obtained on aconventional patterned structure which is prepared from a single sheetmember.

Where each of the plurality of sheet members has the thin-walled portionor portions so that the thin-walled portions of the different sheetmembers are in contact with each other, the total thickness of thesuperposed thin-walled portions can be substantially equal to thethickness of each sheet member. In this case, the superposed thin-walledportions may lie in the same plane as the other portions (non-superposedor comparatively thick-walled portions).

In the case where each of the sheet members has two or more thin-walledportions having different thicknesses, the thin-walled portions mayengage each other without increasing the total thickness of thesuperposed thin-walled portions. For instance, the relatively thickfirst thin-walled portion of a first sheet member contacts therelatively thin second thin-walled portion of another sheet member,while the relatively thin second thin-walled portion of the first sheetmember contacts the relatively thick first thin-walled portion of thesecond sheet member, such that the prepared patterned structure has thetotal thickness of the first and second thin-walled portions which isequal to the nominal thickness of the sheet members, i.e., thickness ofthe other portions of the sheet members.

It will be understood from the foregoing description that the presentinvention provides a precisely patterned structure which has accuratelydimensioned minute voids such as openings, holes or slits whose aspectratio is comparatively small. The patterned structure may be suitablyused as various electrical lead frames, masking members, circuit boards,electrode assemblies, terminal assemblies, connector assemblies, andfilter assemblies. Thus, the present invention is industriallysignificant.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and optional objects, features and advantages of the presentinvention will be better understood by reading the following descriptionof presently preferred embodiments of the invention, when considered inconjunction with the accompanying drawings, in which:

FIGS. 1(a) through 1(g) are explanatory views schematically illustratingone form of a patterned structure and a method for producing the same,according to one embodiment of the invention, FIGS. 1(a), 1(c) and 1(e)being plan views of a first patterned sheet member, a second patternedsheet member, and the patterned structure, respectively, FIGS. 1(b),1(d), 1(f) and 1(g) being cross sectional views taken along lines B--B,D--D, F--F and G--G of FIGS. 1(a), 1(c) and 1(e), respectively;

FIGS. 2(a) through 2(g) are explanatory views showing another embodimentof the invention, FIGS. 2(a), 2(c) and 2(e) being plan views of a firstand a second sheet member, and a patterned structure, respectively,FIGS. 2(b), 2(d), 2(f) and 2(g) being cross sectional views taken alonglines B--B, D--D, F--F and G--G of FIGS. 2(a), 2(c) and 2(e),respectively;

FIGS. 3(a), 3(b) and 3(c) are explanatory views schematicallyillustrating a patterned structure and a method according to a furtherembodiment of the invention, wherein only one of two metal sheet membersis provided with thin-walled portions, FIGS. 3(a) and 3(b) being planviews of the first and second sheet members, and FIG. 3(c) being a planview of the patterned structure;

FIGS. 4(a), 4(b) and 4(c) are explanatory views schematicallyillustrating a patterned structure having openings whose aspect ratio isrelatively small, and a method for producing the same, according to astill further embodiment of the invention, FIGS. 4(a) and 4(b) beingplan views of a first and a second sheet member, and FIG. 4(c) being aplan view of the patterned structure;

FIGS. 5(a) and 5(d) are explanatory plan views of still further forms ofthe electrically conductive sheets according to a still furtherembodiment of the invention;

FIGS. 5(b) and 5(c) are cross sectional views taken along lines B--B andC--C of FIG. 5(a), respectively;

FIG. 5(e) is an explanatory plan view showing an electrode assemblyprepared by superposing the two conductive sheets of FIGS. 5(a)-5(d) oneach other; and

FIGS. 5(f), 5(g) and 5(h) are cross sectional views taken along linesF--F, G--G and H--H of FIG. 5(e), respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To further clarify the concept of the present invention, the presentlypreferred embodiments of the invention will be described. It is to beunderstood that the invention is not limited to the details of theillustrated embodiments.

It is also to be understood that the invention may be embodied withvarious changes, modifications and improvements, which may occur tothose skilled in the art, without departing from the spirit of theinvention.

Referring first to FIGS. 1(a)-1(g), reference numeral 2 denotes a firstpatterned sheet member which is prepared from a metallic sheet. Thefirst sheet member 2 has a generally comb-like configuration whose outerprofile is formed by etching, as indicated in FIGS. 1(a) and 1(b). Thepatterned sheet member 2 has two mutually spaced-apart thin-walled-portions 2a, and three non-etched portions 2b (thick-walled portions) inthe form of elongate strips of the comb-like configuration. Thenon-etched portions 2b are spaced apart from each other in the directionof their width. The thin-walled portions 2a have a thickness which isone half of the nominal thickness of the sheet member 2 (i.e., one halfof the thickness of the non-etched portions 2b). A second patternedsheet member 4 is prepared from another metallic sheet having the samethickness as that of the first patterned sheet member 2. As shown inFIGS. 1(c) and 1(d), the second sheet member 4 has three thin-walledportions 4a and two non-etched or thick-walled portions 4b, which arelocated differently from the portions 2a, 2b of the first sheet member2. The non-etched portions 4b are spaced apart from each other in thedirection of their width. The thin-walled portions 4a also have athickness which is one half of the nominal thickness of the sheet member4. The first and second patterned sheet members 2 and 4 are partiallysuperposed on each other such that the thin-walled portions 2a and 4aengage or contact the non-etched portions 4b and 2b, respectively, so asto accurately position the two sheet members 2, 4 relative to eachother, as indicated in FIGS. 1(e), 1(f) and 1(g). Thus, the two sheets2, 4 are assembled together into a patterned structure 10, wherein thetwo sheets 2, 4 cooperate with each other to define a plurality ofelongate rectangular voids in the form of slits 8 having a very smallwidth.

As is seen from FIG. 1(g), the thus prepared minutely patternedstructure, which has a generally planar shape, has an overall thicknesswhich is about 1.5 times as large as the nominal thickness of thepatterned sheet members 2, 4.

Referring next to FIGS. 2(a)-2(g), there is shown another embodiment ofthis invention. This embodiment uses a first and a second patternedsheet member 12, 14 which have the same outer profiles as thecorresponding first and second sheet members 2, 4 of the precedingembodiment. Unlike the sheet members 2, 4, however, the sheet members 12and 14 have first thin-walled portions 12a, 14a, and second thin-walledportions 12b, 14b, respectively. These first and second thin-walledportions 12a, 14a, and 12b, 14b have different thicknesses. Morespecifically, the thickness of the first thin-walled portions 12a, 14ais one third of the nominal thickness of the sheet members 12, 14, i.e.,one third of non-etched or thick-walled portions 12c, 14c of the sheets,while the thickness of the second thin-walled portions 12b, 14b is twothirds of the nominal thickness of the sheet members 12, 14. Thenon-etched portions 12c of the sheet 12 are spaced apart from each otherin the direction of their width, and the non-etched portions 14c of thesheet 14 are also spaced apart from each other in the direction of theirwidth.

The first and second patterned sheet members 12, 14 are superposed oneach other such that the first thin-walled portions of one of the twosheet members engage or contact the second thin-walled portions of theother sheet member. Thus, a patterned structure 20 is prepared from thetwo sheet members 12, 14, as shown in FIGS. 2(e)-2(g). In thisembodiment, the overall thickness of the patterned structure 20 issubstantially equal to the nominal thickness of the component sheetmembers 12, 14, as indicated in FIG. 2(g).

Reference is now made to FIGS. 3(a), 3(b) and 3(c) which show a furthermodified embodiment of the invention, in which only one of two patternedsheet members 22, 24, namely, only the sheet member 22 has a thin-walledportion 22a. The first sheet member 22 is prepared from a metallicsheet. The metallic sheet is first etched such that the etched sheet hasan outer profile as shown in FIG. 3(a). Then, the etched metallic sheetis subjected to an etching operation so as to form the thin-walledportion 22a whose thickness is one half of the nominal thickness of themetallic sheet. Thus, the first patterned sheet member 22 is produced,with two rectangular cutouts 23 formed therethrough in the first etchingof the metallic sheet such that each cutout 23 is defined by twoadjacent non-etched strip portions 22b which are spaced apart from eachother in the direction of their width. These cutouts 23 cooperate withstrip portions 25 of the second patterned sheet member 24 to define aplurality of elongate rectangular voids in the form of slits 28 whichwill be described.

The second patterned sheet member 24 is prepared from another metallicsheet, so that the sheet member 24 having the strips 25 has an outerprofile as shown in FIG. 3(b). The first and second patterned sheetmembers 22, 24 are superposed on each other such that the portion of thesecond sheet member 24 from which the strips 25 extend is in contactwith the thin-walled portion 22a of the first sheet member 22, and suchthat the cutouts 23 of the first sheet member 22 cooperate with thestrips 25 of the second sheet member 24 to define the slits 28 indicatedabove. Thus, the two sheet members 22, 24 are assembled together into apatterned structure 26 having the narrow slits 28, as shown in FIG.3(c). The slits 28 are formed on opposite sides of each strip 25 of thesecond sheet member 24 which is aligned with the longitudinal centerlineof the corresponding elongate cutout 24 of the first sheet member 22.

Referring next to FIGS. 4(a)-4(c), there is illustrated a still furtherembodiment of the present invention which uses a first and a secondpatterned sheet member 32, 34. Each of these two sheet members 32, 34 isprepared by etching from a single metallic sheet. Both of the sheetmembers 32, 34 have a plurality of rectangular cutouts 36 having arelatively large size. The first sheet member 32 has an etchedthin-walled portion 32a, and a plurality of non-etched or thick-walledportions 32b which overlap the cutouts 36. Similarly, the second sheetmember 34 has an etched thin-walled portion 34a, and a plurality ofnon-etched or thick-walled portions 34b overlapping the cutouts 36. Thethickness of the thin-walled portions 32a, 34a is one half of thenominal thickness of the sheet members 32, 34.

These first and second patterned sheet members 32, 34 are superposed oneach other such that the non-etched portions 32b of the first sheetmember 32 are fitted in the respective cutouts 36 of the second sheetmember 34 while the non-etched portions 34b of the second sheet member34 are fitted in the respective cutouts 36 of the first sheet member 32.Further, the thin-walled portions 32a, 34a of the two sheet members 32,34 are held in contact with each other. As a result, there is produced aplanar patterned structure 40 having an array of small rectangularopenings or voids 38 which are spaced apart from each other.

A still further modified embodiment of the invention is illustrated inFIGS. 5(a) through 5(h), wherein each of two stainless steel sheets 42,44 as electrically conductive sheets has mutually spaced-apart apertures45, each of which have length portions which have different widths.Described more specifically, the apertures 45 and thin-walled portions46 are formed in each stainless steel sheet 42, 44, by an etchingoperation, as in the preceding embodiments. Each aperture 45 has arelatively wide central portion 45a, and relatively narrow opposite endportions 45b, 45b on both sides of the central portion 45a. The ends ofthe opposite end portions 45b are defined by the thin-walled portions46. As a result, the apertures 45 define a plurality of mutuallyspaced-apart, generally elongate electrode portions 48, each of whichhas a relatively narrow central portion 48a, and relatively wideopposite end portions 48b, 48b which terminate in the thin-walledportions 46. The width of the relatively narrow end portions 45b of theaperture 45 is made equal to that of the relatively wide end portions48b of the electrode portion 48. The thickness of the thin-walledportions 46 is one half of the thickness of the electrode portions 48.The two stainless steel sheets 42, 44 are superposed on each other suchthat the wide end portions 48b of the electrode portions are snuglyfitted in the corresponding narrow end portions 45b of the apertures 45,whereby an electrode assembly 50 as shown in FIG. 5(e) is prepared.

What is claimed is:
 1. A patterned structure comprising a plurality ofpatterned sheet members each of which has a plurality of strip portionsspaced apart from each other in a direction of a width thereof, saidpatterned sheet members being partially superposed on each other suchthat said strip portions of said patterned sheet members cooperate witheach other to define a plurality of volts, and such that said stripportions of said patterned sheet members are separated from each otherby said voids, said patterned sheet members having respective areas atwhich the sheet members are superposed on each other, at least a part ofthe area of at least one of said patterned sheet members including athin-walled portion whose thickness is smaller than a thickness of theother portion of said at least one patterned sheet member.
 2. Apatterned structure according to claim 1, wherein each of said patternedsheet members has said thin-walled portion, the thin-walled portions ofsaid patterned sheet members are superposed on each other.
 3. Apatterned structure according to claim 1, wherein said other portion ofsaid at least one patterned sheet member includes said plurality ofstrip portions, said strip portions of one of said at least onepatterned sheet member partially overlapping said strip portions ofanother of said at least one patterned sheet member, when viewed in adirection of thickness of said at least one patterned sheet member suchthat said patterned structure has a thickness which is substantiallygreater than said thickness of said strip portions.
 4. A patternedstructure according to claim 1, wherein said other portion of said atleast one patterned sheet member includes said plurality of stripportions, said patterned structure having a thickness substantiallyequal to said thickness of said other portion of the patterned sheetmembers strip portions.
 5. A patterned structure according to claim 1,which is a lead frame having a plurality of electrical lead portionseach of which includes at least a part of a corresponding one of saidstrip portions of said patterned sheet members.
 6. A patterned structureaccording to claim 1, wherein each of said plurality of strip portionsof said patterned sheet members consists of a generally elongate strip.7. A patterned structure according to claim 6, wherein each of saidplurality of voids consists of a slit having a width smaller than saidthickness of said strip portions.
 8. A patterned structure comprising aplurality of patterned sheet members each of which has a plurality ofcutouts, said patterned sheet members being partially superposed on eachother such that said cutouts of one of said patterned sheet memberspartially overlap said cutouts of another of said patterned sheetmembers, so that a plurality of mutually spaced-apart voids are definedby overlapping portions of said cutouts of said one patterned sheetmember and said another patterned sheet member, said patterned sheetmembers having respective areas at which the sheet members aresuperposed on each other, at least a part of the area of at least one ofsaid patterned sheet members including a thin-walled portion whosethickness is smaller than a thickness of the other portion of said atleast one patterned sheet member.
 9. A patterned structure according toclaim 8, wherein each of said patterned sheet members has an etchedportion as said thin-walled portion, and a plurality of non-etchedportions as said other portion, each of said non-etched portions of oneof said patterned sheet member being fitted in said plurality of cutoutsof another of said patterned sheet members, respectively, such that saidvoids are left in said overlapping portions of said cutouts of said onepatterned sheet member and said another patterned sheet member.
 10. Apatterned structure according to claim 8, wherein each of said pluralityof cutouts is a rectangular cutout, and each of said voids is arectangular void.